Nonlinear optical materials can change the intensity and phase of light in response to an external field such as an electric field and a magnetic field and are therefore practically used as optical control elements in optical communication equipment, laser apparatus, and the like. Inter alia, devices such as optical modulators, optical switches, and optical memories utilize the electrooptic effect of non-linear optical materials.
Conventionally, as nonlinear optical materials, inorganic materials such as lithium niobate and potassium dihydrogen phosphate have been widely used. However, the demands for higher nonlinear optical performance, manufacturing cost reduction, composites with an electronic integrated circuit, and the like have led to increased attention on organic nonlinear optical materials and various investigations into their practical use have been conducted, as described in “Hisenkei Kougaku No Tameno Yuuki Zairyo (Organic Materials for Nonlinear Optics)”, edited by the Chemical Society of Japan, KIKAN KAGAKU SOSETSU No. 15 (1992); “Organic Nonlinear Optical Materials”, Ch. Bosshard, et al., Gordon and Breach Publishers (1995); and “Joho, Tsushin Yo Hikari Yuuki Zairyo No Saishin Gijutsu (The Newest Technology of Optical Organic Materials for Information and Telecommunication)”, supervised by Toshikuni Kaino, CMC Publishing CO., LTD., 2007.
Organic nonlinear optical materials are obtainable by dispersing in or binding to a host material (e.g., a polymeric material) a compound having nonlinear optical activity (hereinafter simply referred to as a “nonlinear optical compound”). A known nonlinear optical compound that exhibits the electrooptic effect is a push-pull π-conjugated compound having an electron donor group (donor structure D) and an electron acceptor group (acceptor structure A), which are present at either end of the molecular structure, as well as a π-conjugated chain (π-conjugated bridge structure B) that connects said groups. For example, U.S. Pat. No. 6,067,186 describes a nonlinear optical compound having a thiophene ring in a π-conjugated bridge structure B, as represented by the following formula:

JP 2004-501159 T describes an attempt to improve the performance of a nonlinear optical compound by employing a predetermined group as an acceptor structure A. “Large Electro-optic Activity and Enhanced Thermal Stability from Diarylaminophenyl-Containing High-β Nonlinear Optical Chromophores.” Y. J. Cheng, et al., Chem. Mater. Vol. 19, 1154 (2009) also describes an attempt to improve the performance of a nonlinear optical compound by employing a predetermined group as a donor structure D.